Seismic Testing May Have Major Impact On Concrete Wall Construction

Thursday, 27 April 2023, 2:35 pm
Press Release: Earthquake Commission

Research into the technique used to connect reinforced
concrete walls to their foundations is set to have a
significant impact on the New Zealand construction
industry.

Researchers at the University of Canterbury
are conducting earthquake testing to better understand the
performance of a construction technique called staggered
lapsed splices, which is used to connect the steel bars in
reinforced concrete walls to the steel bars coming out of
the foundations.

The practice is no longer used
overseas, but allowed under the New Zealand building
code.

“The connections between the walls and the
foundation are created by overlapping the steel bars and
they rely on the concrete around the bars to transfer the
seismic forces from one bar to the other,” explains lead
researcher Professor Santiago Pujol from the Department of
Civil Engineering, whose research has been funded by Toka
Tū Ake EQC.

“This configuration is economical and
easy to build but does not always provide the toughness for
the walls to resist the demands of an earthquake,” says
Pujol, who adds that structures using this configuration
have collapsed in previous earthquakes in Turkey, Chile,
Japan and Alaska.

“When these connection fails, the
outcomes are often catastrophic.”

Pujol says that
New Zealand has fortunately not seen similar catastrophic
failures of lapsed spliced walls in the Canterbury and
Kaikōura earthquakes, but is vital to test the seismic
strength of staggered lap splices in a controlled
environment.

PhD student Charlie Kerby is carrying out
the testing at the Seismic Engineering Laboratory by
attaching the walls to hydraulic actuators which mimic the
effects of a major earthquake by pushing and pulling the
walls until they fail.

“We are not interested in how
much force is needed to make the wall fail, but how much the
wall can deform before failure occurs,” says
Kerby.

“Buildings need to be able to move with the
earthquake and we are looking at how much a lap splice can
deform until it fails.”

The research is funded by
Toka Tū Ake EQC as part of its contestable Biennial Grants,
which supports research in improving the resilience of
buildings to New Zealand’s natural hazards to better protect
people and property.

“Our organisation invests
around $19 million each year into research to better
understand our natural hazards. Professor Pujol’s project
is a great example of research that identifies potential
risks, but also informs better engineering solutions for
reinforced concrete buildings, which many of us live and
work in,” says Dr Jo Horrocks, Chief Resilience and
Research Officer at Toka Tū Ake EQC.

University of
Canterbury researcher Charlie Kerby explains that engineers
have alternative options like welding the steel bars
together or using a mechanical connection to transfer
seismic forces, but says that tradition and economics
dominate most of what happens in the construction
industry.

“These lap splices have been used for over
a century and from an economic viewpoint, an extra meter of
steel virtually costs nothing compared to a specifically
designed connection.”

Kerby says that the question
whether lap splices actually perform well in earthquakes has
only been raised fairly recently, so the research at the
University of Canterbury will provide vital new insights to
inform engineers and construction standards.

Professor
Pujol says that his team will not only put the spotlight on
a potential problem but also provide solutions for the
industry by designing and testing alternative
configurations.

“We will find out what works best to
enable greater confidence in building
design.”

© Scoop Media


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